KBB isn't kind, the furthest they go back is 91 and one in excellent condition is only $2350usd.
That one is borderline classic in what looks to be excellent condition, however I still wouldn't see it bringing more than $3000 on a good day to the right buyer (private sale). I've seen/bought them myself in comparable condition/vintage for under $2000. As aggravating as it is (or for me, isn't), they really just aren't worth that much.........yet. Keep in that shape/mileage for another 15-20 years and then you have something. Until then though it's just a old German sedan that happens to be in really nice shape.
Maybe comb through the local classifieds and check online sources to find a reasonable price and offer the others a 1/3 each of what you find? If they're concern is it's worth a pile of cash though. Right now it isn't